Srinivas Kasulla

Biogas, which is obtained by anaerobic decomposition of organic material, contains not only methane (CH₄) and carbon dioxide (CO₂), but also a number of other impurities. These impurities can affect the quality and usability of biogas. Here are some common impurities and their effects: 1. Carbon dioxide (CO₂) Impact: CO₂ reduces the energy value of biogas. Pure methane has an energy value of about 35-40 MJ/m³, while CO₂ does not provide energy. Solution: CO₂ removal is key to improving the energy density of biogas.

2. Water vapor (H₂O) Impact: Moisture in biogas can cause corrosion in equipment and reduce the efficiency of fuel systems. Solution: Dehydration of biogas using different methods (eg cooling, adsorption) is important for quality improvement.

3. Hydrogen sulfide (H₂S) Impact: H₂S is a corrosive and toxic gas that can cause serious damage to engines and other devices. It is also a health hazard. Solution: Removal of H₂S is necessary, usually using chemical or biological methods.

4. Ammonia (NH₃) Impact: Ammonia can affect the quality of biogas and pose a problem for engines, but also for wastewater treatment. Solution: Purification by adsorption method or chemical reactions.

5. Solid solid residues (TSS) Impact: Solid debris can block treatment systems and reduce the efficiency of energy production. Solution: Filtration and separation of solids before processing.

6. Volatile organic compounds (VOCs) Impact: VOCs can be toxic and affect the quality of biogas, as well as the environment. Solution: It is necessary to remove or minimize VOCs before using biogas.

Management of impurities in biogas is crucial for improving its quality and maximizing its energy potential. Effective purification not only improves energy density, but also extends equipment life and reduces risks to health and the environment.

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Werkneh AA. Biogas impurities: environmental and health implications, removal technologies and future perspectives. Heliyon. 2022 Oct 6;8(10):e10929. doi: 10.1016/j.heliyon.2022.e10929. PMID: 36299513; PMCID: PMC9589174.

[Abstract

Biogas is a promising bioenergy alternative to be recovered from waste/wastewater in the context of environmental sustainability and circular economy. However, raw biogas contains various secondary impurities such as carbon dioxide, hydrogen sulphide, siloxanes, nitrogen oxides (NOx), ammonia, and halogens. Depending on the emission rate of these biogas impurities, the importance of biogas is being hampered for its environmental, health and the detrimental effects possess by the impurities towards the downstream of the biogas users. Biogas impurities can cause different public health concerns (like pulmonary paralysis, asthma, respiratory diseases and deaths) and environmental impacts (such as global warming, climate change and their indirect impacts like drought, flooding, malnutrition and other disasters). The absence/inconsistent emission standards among countries, agencies, and other stakeholders is the other challenge that they possess during monitoring and controlling of these impurities. Different commercially available and emerging technologies are available for separating carbon dioxide (via biogas upgrading) and removing other biogas impurities. Technologies such as pressure swing adsorption, membrane separation, absorption-based techniques (water, chemical and physical organic solvents), cryogenic separation, and other emerging biotechnological platforms (like photobioreactor and biocatalysis) have been adopted in removing the impurities.]